1. Field of the Invention
The invention is directed to high resolution printing on edibles using an ink-jet printer and dispersed pigmented inks. The system provides for rapid turnaround from image input to printed edible product. Methods of printing, ink formulations suitable for use with the methods, site-vending and e-commerce applications are all described herein, and are within the intended scope of the invention.
2. Description of the Related Art
Highly detailed images can be formed on chocolates using a pad printing process. In this process, the substrate is contacted with an inked pad having the image formed thereon. Sometimes, in order to prepare an image having greater resolution, the chocolate is contacted repeatedly with the pad. An example of a pad printing process is described in CA 2,057,985. While, the pad printing process can deliver highly detailed images it cannot be adapted for rapid turnaround applications. Each requested change to an image requires that a corresponding change be made to the printing pad or the manufacture of a new pad which means that pad printing will have a slow turnaround time. One object of the invention, therefore, is to provide for rapid turnaround printing of high resolution images on edibles.
Ink jet printing systems are generally of two types: continuous jet and drop-on-demand. In continuous jet ink jet systems, ink is emitted in a continuous stream under pressure through at least one nozzle. The stream is broken up into droplets at a fixed distance from the orifice. Typically, the ink droplets in continuous ink jet systems are formed by a piezoelectric crystal, which is vibrated at controlled frequency adjacent to the ink stream. To control the flow of ink droplets, these inks are charged (by addition of salts and other conductive agents) and relayed in accordance with digital data signals. The droplets are passed through an electrostatic field, which adjusts the trajectory of each droplet. The droplets are either directed back to a gutter for recirculation or to a specific location on the substrate to create the desired character matrix.
In drop-on-demand systems, a droplet is expelled under pressure from a valve directly to a position on the substrate in accordance with the digital data signals. A droplet is not formed or expelled unless it is to be jetted to the substrate. The formation of droplets in drop-on demand systems can either be achieved by a piezoelectric crystal (similar to continuous jet systems) or by a thermal (bubble-jet) technique. The latter technique involves formation of ink droplets by thermally heating ink in the cartridge reservoir thereby forcing ink to be expelled in an “on-demand” basis. Typically, drop-on-demand systems print at a slower rate than continuous jet systems (due to time required to make droplets on demand) but produce higher resolution images. However, some of the commercially available printhead units (for example, manufactured by Xaar, Trident and Picojet) achieve high throughput rates even with drop-on-demand systems by using their proprietary technologies. Also, since drop-on-demand systems require no ink recovery, charging, or deflection, these systems are simpler than the continuous stream systems.
Further, continuous jet ink-jet printing systems do not yield the same high resolution images that can be obtained with drop-on-demand ink-jet systems. A typical maximum resolution for a continuous jet printer image on an edible substrate using a single printhead and a single pass printing is about 70-90 dpi.
Published European Patent Application EP 705 890 A1 discloses an ink for use with a continuous ink jet printer. The ink comprises pigment, such as titanium dioxide; binder, such as shellac or poly(1-vinyl-2-pyrrolidone); and an aqueous carrier. The binder is apparently required to increase the compatibility of the inked image with the substrate in the continuous ink-jet environment contemplated.
Other methods of decorating edibles are known in the prior art. UK Patent GB 2,291,838 B describes a machine and method for printing on an edible substrate. This patent discloses a generic ink-jet/bubble-jet head assembly together with a stepping motor for moving the head assembly. A pump provides food coloring to the head assembly from ink reservoirs. A computer provides the instructions for printing on the edible substrate.
Food colorings which are dye-based systems behave differently than dispersed pigmented inks in an inkjet environment, and exhibit profoundly different image characteristics on edible substrates. Dye-based inks possess limited opacity and therefore do not hide dark background colors, such as milk chocolate and dark chocolate surfaces. Also, dye-based inks are not available in all colors. For example, white ink is not available as a dye system but is available only as a pigmented (dispersed) system.
The examples of the prior art do not describe methods or systems to print high resolution images on edibles using an ink-jet printer and pigmented inks. There is also no description of a system or method wherein a consumer can participate in the selection and customization of an edible product with a high resolution image and subsequently receive the customized product in rapid fashion.